A substrate having a flow channel of 100 μm or less processed by a microfabrication technique used for semiconductor is generally called “microchip”, and attention has been recently focused on micro-nanochemistry (micro-nanotechnology) of integrating various kinds of chemical and/or biochemical processes, such as analysis, synthesis, and cellular experiment, using such a substrate.
In order to define a flow direction of a fluid through a flow channel of a microchip and to control a flow of the fluid, a mechanical fluid-controlling device, such as a valve or a pump, is provided on a flow channel. Japanese Patent Application Publication No. 2005-083510 (published on Mar. 31, 2005) discloses a slide-type valve that uses slidable glass substrates to switch back and forth between several flow channels. Japanese Patent Application Publication No. 2005-013980 (published on Jan. 20, 2005) and K. Morishima et al. Proc. Micro Total Analysis Systems 2003: 1033-1036 (2003) disclose devices in which a flow in a flow channel is stopped by a needle-type metallic pin inserted into the flow channel.
The valve disclosed in Japanese Patent Application Publication No. 2005-083510 is superior in that the valve involves very little dead volume. Despite such an advantage, this valve has the following problems. That is, the valve requires movement of a glass substrate itself and thus limits a design of a flow channel, resulting in difficulty in juxtaposition and automatization of the valve. Further, the valve has difficulty in being used with an organic solvent and difficulty in being used under a high pressure exceeding 100 kPa. This is because hydrophobic modification with a fluorine coating agent or the like is applied on gaps besides the glass substrates in order to prevent leakage of water through the gaps.
On the contrary, the device described in Japanese Patent Application Publication No. 2005-013980 and the device described in K. Morishima et al. Proc. Micro Total Analysis Systems 2003: 1033-1036 (2003) are each able to block a flow channel at a single point and can be relatively easily juxtaposed and automatized, as compared to the valve described in Japanese Patent Application Publication No. 2005-083510. However, the device described in Japanese Patent Application Publication No. 2005-013980 and the device described in K. Morishima et al. Proc. Micro Total Analysis Systems 2003: 1033-1036 (2003) inevitably involve the formation of a gap between a needle and a glass, and thus requires hydrophobic modification on such a gap. This results in the same problem as in Japanese Patent Application Publication No. 2005-083510.
Since glass is an extremely firm material, it is not easy to construct a fluid-controlling device with glass, and it is very difficult to mount a glass fluid-controlling device on a glass substrate. In view of this, a polymeric material typified by polydimethylsiloxane (PDMS) has been recently used as a material for a fluid-controlling device to be used for a microchip. PDMS is very inexpensive, is easy to be processed, and is rich in bendability. A microvalve mechanism as shown in FIG. 12 is known in which a PDMS fluid element chip 12, having a circular hollow part 13 and a microflow channel extending across the circular hollow part 13, is provided so as to face a glass substrate 11 (Japanese Patent Application Publication No. 2005-308200 (published on Nov. 4, 2005). The microvalve mechanism is arranged such that the fluid element chip 12 is deformed by application of pressure from a pressing member 19 so that the circular hollow part 13 permits passage and blocking of a fluid through the microflow channel.